This invention relates to the field of submersible electric motors for pumping fluids from wells. In many instances it is desirable to be able to increase the total output horsepower of submersible motor-pump systems, which can be accomplished by assembling motors in tandem configuration. However, difficulties arise that are not ordinarily encountered when using a single enclosed submersible motor. During the assembly of the tandem motors, above ground, before being placed into the well, problems arise in making proper electrical interconnections between the two tandem motors and in the opening of and the interconnection of the oil flow channels between the two motors. To expose the motor oil to the atmosphere enhances the opportunity for contaminant material and/or loss of oil.
Each submersible motor contains an oil circulation path for lubrication and cooling purposes. When submersible motors are connected in tandem the oil co-mingles. Hence, failure of one motor will tend to degrade the other motor so that all will have to be replaced. This is often due to the failing motor tending to produce contaminating material, which is circulated through the oil flow channels and, thus will affect the operation of all the motors.
In addition, during in-the-well service, the longitudinal drive shaft expands, which thermal expansion is multiplied in tandem motor assemblies. This expansion places stresses upon the shaft and thrust bearings ordinarily used in submersible motor assemblies. Although the shafts are coupled by means that allow for expansion, rotary motion of the shaft does not permit sliding longitudinal movement within such couplings. Also, vibration problems exist which have not heretofore been encountered in a single motor assembly.